The present invention relates to a single in-line type semiconductor device having external leads extending therefrom in staggered fashion.
An example of a power IC for use in audio control, motor control or the like, is a single in-line package (hereinafter referred to as SIP) type which has external leads extending from only one end face of the package. This SIP type IC can be classified into two types:
(1) a lead straight type having external leads arranged in a row, and
(2) a staggered type having every other external lead bent, so that the external leads are arranged in two rows in staggered fashion.
FIG. 1 is a perspective view illustrating the outline of a conventional staggered type IC. In the drawing, numeral 10 is a package made of insulative resin, ceramic, or the like. This package 10 is provided with a pair of notches 11 through which screws are fitted to fix an external heat discharge plate to the package. Further, a metal heat discharge plate 12 is embedded in one surface of this package 10. Though not illustrated, a semiconductor pellet is disposed on discharge plate 12 within package 10. A plurality of external leads 13 formed by stamping a metal plate are drawn out from the bottom edge portion of package 10, and are arranged in two rows in staggered fashion with every other external lead being bent. That is, individual leads 13A in one of these two rows extend vertically from the bottom edge portion of package 10, and the remaining leads 13B in the other row, each arranged adjacent to its corresponding external lead 13A, are bent as illustrated. The free ends of these leads 13 are formed narrow, so as to be insertable in openings or through-holes formed in a printed circuit board (not shown). A so-called positioning portion 14 is provided at the boundary of the narrow portion and the remaining wide portion of each lead 13. This positioning portion 14 is provided to prevent each lead 13, when inserted, for soldering, in the through-hole of the printed circuit board, from penetrating deeper than that boundary position, thereby determining the position, and mainly the height, of the IC.
Conventionally, in forming the positioning portion 14, the individual leads are formed through a stamping process first without bending any, so that their narrow portions have the same length, and then every other lead is subjected to a bending process. According to the prior art, therefore, as is shown in FIG. 2, the linear length L1 of each external lead 13A which is not bent from the bottom edge portion of package 10 to its positioning portion 14 is longer than the linear length L2, of each bent external lead 13B. The positioning portions 14 of bent external leads 13B do not therefore contribute to the positioning of the IC at the time it is soldered on the printed circuit board.
In soldering such an IC on a printed circuit board, a solder layer coating known as a solder dip is performed on the external leads, in advance, to facilitate an easier soldering operation. As a result of this solder dip being carried out, a solder ball 16 is formed on the inner side of a bent portion 15 of each bent external lead 13B, as shown in FIG. 3 (side view). This solder ball 16 is formed with a large variation, so that package 10 may be fixed inclined to a printed circuit board 17 at the time external leads 13 are fitted, for soldering, in the openings of printed circuit board 17. If package 10 is fixed in such an inclined state, when screws are fit through notches 11 to fix the package to an external heat discharge plate 18, the package will be subjected to stress generated by the screwing action. As a result, cracking may occur in the semiconductor pellet (not shown) inside package 10, or wiring lines on board 17 may become separated therefrom when it is attempted to forcibly settle the package 10 straight.